The present invention relates to apparatus for stitching along the line parallel to an edge of a supple workpiece and comprising:
a machine such as a sewing machine;
a drive device for moving the workpiece, including the feed dog and pressure foot of the sewing machine;
a worktable for supporting the workpiece;
and a correction device for detecting the workpiece and including recentering means controlled by the detection device for moving the workpiece in the desired manner.
French Pat. No. 2,525,008 discloses recentering means which is comprised of a turntable having a plurality of shoes applied to the workpiece during treatment. The installation described therein is complicated and required that the workpiece be held flat to prevent creasing.
French Pat. No. 2,457,920 discloses recentering means rotated by drive means under the control of an action device to follow a curved edge but is not cable of following a changing profile such as one having a successive convex/concave curvature nor is the apparatus usable to treat workpieces of reduced dimensions.
The present invention overcomes the disadvantages of the prior art by providing recentering means comprising an active guide and drive means cooperating to move the workpiece.
The workpiece is initially delivered to the worktable whereupon the detection device controls the recentering of the workpiece by displacement of the active guide and the movable support either alone or in combination. The aforesaid installation compared with conventional installations provide more precise recentering.
The detection device comprises first and second detectors arranged between the drive device of the sewing machine and the active guide. A third detector is located upstream relative to the active guide and remote from a reference line parallel to the treatment line and tangential to the edge of the workpiece at the point of treatment.
In those cases where the workpiece has a convex edge, four detectors are employed, the fourth detector being located upstream relative to the active guide and to the left of the aforesaid reference line.
In a preferred embodiment, the first two detectors are arranged to be symmetrical with respect to the reference line. Similarly the third and fourth detectors are placed so that they are symmetrical with respect to the reference line for cases in which four detectors are employed.
The active guide includes a rotating member comprised of a plurality of disc-shaped elements arranged for movement about the periphery of a rotating member and engaging the workpiece to impart movement thereto.
The rotatable support rotates about a perpendicular axis, as is described in French Pat. No. 2,457,920 and may alternatively consist of an endless belt whose upper run lies in the plane of the worktable and forms a continuation thereof.
There exist certain situations in which the workpiece recentering means operates in an unsatisfactory manner. As one example, when the edge of the workpiece lies to close to a portion of the sew line, the recentering means automatically follows the edge of the workpiece without stopping the sewing operation at the spot desired for the end of the sewing operation. As another example, in cases where supple workpieces formed of knitted fabrics undergo considerable rotation, the knitted fabric becomes deformed. These problems are incapable of being overcome by the conventional apparatus described herein.
The present invention overcomes the above-mentioned problems by providing a counting device for counting the stitches along the selvage which may be generated by the reciprocating action of the sewing machine needle arm.
The counting device controls the action of the recentering means by holding the turntable drive means and lifting the active guide when the counting devices reaches the predetermined count which is a function of the length of the sew line.
The digital count may correspond to the number of stitches necessary for providing a seam along a distance slightly less the total length of the edge to be sewn. The detection system may be of the reflector type which is mounted on the active guide in such a way as to be positioned opposite a photoelectric sensor.
When the count reaches a given number, the counting device stops the turntable drive means and lifts the active guide to permit linear stitching.
For safety purposes, a retractable guide stop may be added to the counting device to permit the end of the sewing operation while the edge of the workpiece is guided by the guide surface of the guide stop.
In a second embodiment, the drive device for displacing the workpiece may be comprised of means for varying the advance of the workpiece arranged at a location upstream relative to the point of treatment.
In particular, in the case of a seam, the sewing machine comprises a differential feed dog whose adjustment is controlled during sewing by the counting device. This embodiment is particularly well adapted to control the deformation of a knitted fabric during sewing. For a given type of workpiece, of which the location of the wales of stitches with respect to the edge to be sewn is known, the adjustment of the differential feed dog is predetermined as a function of the expected deformation of the knitted fabric during sewing; and adjustment during sewing is controlled by the counting device as a function of the number of stitches counted from the beginning of sewing.